1. Field of the Invention
The present invention relates to an image pickup apparatus, an image pickup system, an image pickup method and a computer readable non-transitory recording medium.
2. Description of the Related Art
A conventional technique is known, which uses plural high-speed cameras to continuously take images of fast-moving phenomena in synchronization. The fast-moving phenomena include blasts, crashes, burning, crackups and electric discharges.
FIG. 5 is a conceptual diagram for explaining a conventional image pickup system 1, which uses plural image pickup apparatuses to take images in synchronization. The image pickup system 1 consists of the image pickup apparatuses 10a, 10b. The image pickup apparatuses 10a, 10b are used as a master device and a slave device, respectively. When a shutter key is pressed, the image pickup apparatus 10a, at the same time, sends a shutter command to the image pickup apparatus 10b and takes a picture of an object 12 to obtain image data, performing a still image recording process on the image data to record as a pickup image 11a. Meanwhile, when receiving the shutter command from the image pickup apparatus 10a, the image pickup apparatuses 10b takes a picture of the object 12 to obtain image data, performing the still image recording process on the image data to record as a pickup image 11b. 
But in the conventional image pickup system 1, since a time lag in data sending and receiving processes and a variation of the time lag are caused in and between the image pickup apparatus 10a and the image pickup apparatuses 10b, it is hard to synchronize the pickup images 11a, 11b. For example, it is almost impossible to obtain a synchronization accuracy of 1/1000 sec.
Japanese Unexamined Patent Publication No. 2009-296323 discloses a technique, which makes plural high-speed cameras take images in synchronization. This conventional technique uses one master camera and plural slave cameras connected to the master camera, and makes the master camera transfer an image synchronizing signal for a high-speed camera to the plural slave cameras, bringing their shooting operations in synchronization.
In the above conventional technique, the master camera is provided with a timing adjusting unit for securing an accurate synchronization. The timing adjusting unit uses a pulse signal to measure a delay time along a transferring route from the master camera to the slave camera, and compensates for the delay time using the measurement result. The conventional technique is used to continuously take images of the fast-moving phenomena such as blasts, crashes, burning, crackups and electric discharges. The conventional technique provides a camera system, which is able to take an image at an extremely high speed of 1,000,000 frames per second and belongs to a classification of the high-speed cameras for the professional use.
But the conventional technique disclosed by Japanese Unexamined Patent Publication No. 2009-296323 involves a problem that requires an accurate and troublesome setting before taking pictures. For example, it requires to previously prepare the pulse signal to measure a delay time for making compensation. In general, this technique has another problem that the technique is too complex for consumers to use in dairy life.
When a method of using a pulse signal to measure a delay time is applied a radio transferring route, an uncertain delay is invited in a digital radio transferring route due to sampling and packet operations, preventing an accurate measurement.
In an analog radio transferring route, the accurate measurement can be made, but a multiple communication between the master device and slave devices is not allowed. Therefore, the same number of radio communication devices as the slave devices have to be provided at the master device, which also invite a problem that increases the cost and power consumption.